The present invention relates to an ignition timing control device for an internal combustion engine which controls the ignition timing of the engine in response to detected knocking of the engine.
Ignition timing control devices are known in which a knocking signal is produced in response to the vibration of the engine and variations in the pressure within an engine cylinder, a determination is made as to whether knocking has occurred on the basis of the knocking signal, and, if knocking has occurred, further knocking is prevented by retarding the ignition timing.
A conventional arrangement of such an ignition timing control device is illustrated in FIG. 1 of the accompanying drawings. The illustrated ignition timing control device includes a knocking sensor 1 for detecting knocking of an engine, a reference voltage generator 2 for generating a reference voltage dependent on the level of an output signal from the knocking sensor 1, and a comparator 3 for comparing the level of the output signal from the knocking sensor 1 with the reference voltage from the reference voltage generator 2.
The output signal from the comparator 3 is integrated by an integrator 4. In response to the output signal from the integrator 4, an ignition timing controller 5 determines the ignition timing according to parameters such as the speed of the engine and the engine load conditions.
FIGS. 2(a) to 2(c) illustrate the operation of the device shown in FIG. 1. As shown in FIG. 2(a), the output signal from the knocking sensor 1 has a vibratory waveform. When there is no knocking, the knocking sensor 1 produces a noise signal of a relatively low level as indicated by a. When knocking occurs, the knocking sensor 1 generates a signal of a larger amplitude in synchronization with the occurrences of knocking.
In response to the level of the noise signal produced by the knocking sensor 1, the reference voltage generator 2 generates as a reference voltage a DC voltage which is slightly higher in level than the noise signal, as indicated by b in FIG. 2(a).
The comparator 3 compares the output signal from the knocking sensor 1 with the reference voltage issued from the reference voltage generator 2. When no knocking is present as shown in FIG. 2(b), the output signal from the knocking sensor 1 contains noise components only and does not exceed the level of the reference voltage from the reference voltage generator 2. Therefore, the comparator 3 generates no output signal at all as shown in FIG. 2(b). When knocking occurs, the output signal from the knocking sensor 1 contains a large-amplitude component in addition to the noise signal, and hence exceeds the reference voltage level. Accordingly, the comparator 3 issues a train of pulses in response to the knocking dependent large-amplitude signal as shown in FIG. 2(b).
This integrator 4 integrates the pulse train and produces an increasing output voltage as shown in FIG. 2(c). The ignition timing controller 5 retards the ignition timing to prevent engine knocking from being produced in an amount dependent on the output voltage level from the integrator 4. When the knocking stops, the output voltage level of the integrator 4 drops at a prescribed rate to advance the ignition timing to an original angle.
It has been the general practice in such an ignition timing control system to increase the speed of retarding the ignition timing in order to raise the control response rate at the time of knocking, and also to lower the speed of advancing ignition timing to the original angle in order to provide better stability for controlling at knocking limits. In providing such settings, however, suitable control operation is unable to be obtained, particularly, if the engine speed or load conditions change in a short period of time at the time of acceleration. FIG. 3 illustrates one such varying knocking generating condition.
FIG. 3(a) shows the waveform of an output signal from the knocking sensor 1, the waveform being indicative of a knocking generating condition. FIG. 3(c) illustrates an output voltage generated by the integrator 4 when knocking occurs as shown in FIG. 3(a), the output voltage being representative of the manner in which the ignition timing is retarded.
During an initial knocking interval (A) indicated in FIG. 3(a), the ignition timing is retarded with a good response to suppress knocking immediately. However, since the output voltage from the integrator 4 drops at a relatively low rate in a knocking-free interval (B) in FIG. 3(a), the ignition timing remains retarded unnecessarily even after knocking has already been eliminated. This leads to a problem in that the acceleration response of the engine is deteriorated.